Apparatus for carrying out electrometric analyses



m 17, 1935. u. EHIIQHARDT 2,024,819

APPARATUS FOR CARRYING OUT ELECTROMETRIC ANALYSES Filed March 27, 1929 2 Sheets-Sheet 1 FIG. 1

. .ghujcnfoz,

61 f-to'wmiaa.

U. EHRHARDT Dec. .17, 1935.

APPARATUS FOR CARRYING OUT ELECTROIETRIC ANALYSES Filed llarch27, -1929 2 Sheets-Sheet 2 FIG. 2.

Ema/WM:

Patented Dec. 17, 1935 UNITED STATES PATENT OFFICE APPARATUS FOR CARRYING OUT ELECTROMETRIC ANALYSES tion of Germany Application March 27, 1929, Serial No. 350,384

In Germany April 3, 1928 2 Claims.

This invention'relates to an apparatus for carrying out electrometric analyses with the aid of electron tubes. Apparatus based upon this principle are old in themselves Goode (Am. Soc. 44, 26

, (1922)) published, as early as in the year 1922,

a paper describing a continuous reading potenti ometer which, however, was only adapted for determining PH constants. In the year. 1925 Treadwell (Helvetica Chimica Acta 8, 89 (1925)) showed, based upon C. Paolonl's experiments, that chlorine ions can be titrated by means of silver nitrate. However he himself admitted this method to be rather inexact. This inexactness was due to the mode of connection used. Treadwell v further proved by some examples that his method was applicable to conductometric titrations. Finally Williams and Whitenack (Journ. Physical Chem. 31, 519-24, Madison (Wisc.) Chemisches Zentral-Blatt 98 page 3111 (1927)) have recently described a similar device and have remarked that titrations of different kinds, especially pxidimetric ions, gave satisfactory results.

Although these observations were most valuable in scientific respects, they were less important for practical analysis. With the numerous appliances based upon the principle of the Poggendorf compensation method they shared the drawback that -high-ohmic measuring instruments (millivoltmeters) were employed in which only minute currents are used so that an utmost careful manipulation was required. Furthermore, with these appliances only a very small part of the large measuring range of the instruments was utilized for measuring; therefore the jump at the conversion point was recognizable only with difiiculty.

Finally no author has hitherto attached value to the fact that the titration vessel must be given a practical shape. Anyone who has done practical potentiometric work knows the diflic'ulties which arise from the necessity of again and again reliably re-arranging and re-connecting, from case to case, the switch, the calomel electrode, the indicator electrode and the stirrer; especially when the volume of the analytic solution greatly varies.

An object of my present invention is to provide an apparatus for electrometric analysis which, in contradistinction to the apparatus hitherto used, will also suit the requirements of plant laboratory work. This is attained by employing a measuring instrument which, although being extremely reliable with respect to its measuring accuracy, will not, at the same time, require diflicult and subtle handling of the delicate millivoltmeters otherwise employed exclusively. This, however, necessitates a fundamental change in the mode of connection. Furthermore, an apparatus of this kind should be equally applicable to large and small quantities of liquid and should be made suitable for all kinds of electrometric analysis by employing a simple commutation method. To attain these ends I proceed as follows:

The titration potential difference arising between the indicator electrode and the mercury of the calomel electrode is lead ofi in the wellknown manner by means of copper wires and is applied to the negative end of the heating filament of the electrode tube and to the grid of said tube respectively. When this potential suddenly changes at the conversion point, the needle of the milliammeter in the anode circuit is seen shifting. The continuous current of this circuit amounts to 10-20 milliamperes, according to the construction of the electron tube. Now, for obtaining the maximum sensitivity of the instrument, a constant counter-current of corresponding strength is sent in the opposite direction by means of a 2 volt accumulator and a regulable resistor of 500 ohms capacity, a. measuring instrument being employed, the range of which goes from 0 to 1 milliampere, or better from -0.2 to +0.2 milliampere.

By this most simple mode of connection the following important advantages are attained:

1. The whole anode current is utilized for measuring purposes. This current having a rather considerable intensity, I may employ measuring instruments having a small inner resistance (100 to 150 ohms). Such instruments rapidly set will bear a certain amount of rough handling. Instead of the most cumbersome millivoltmeter, which must be exactly adjusted by means of a hydrostatic level, and of which the horizontal dial can only be read with difiiculty, I may use vertical instruments of the switchboard type having a coarse easily distinguishable needle and placed in such a manner that the titration bulb and themeasuring instrument can be supervised simultaneously.

2. Moreover almost the whole measuring range of the instrument is utilized for measuring purposes. For when, for instance, the titration potention changes at the conversion point by 0.2 volt on the addition of one drop of the titration soluticn-which is not uncommon in practice-the anode current changes at a slope (4-) of 2.2 by 0.44 milliamperes, i. e. owing to the fact 'Change of anode current (+yslope Change. of grid voltage that with the compensation method only this difference is measured, the needle travels over one half of the whole scale, whereby the art of measuring is extremely subtilized.

3. Furthermore the possibility of controlling the compensation current affords an utmost convenient means for directing the needle towards that part of the scale where it may most easily be observed. For instance, when an ascent of the needle is expected, the same is directed towards the lower part of the scale, and vice versa. when the needle is on the point of travelling beyond the measuring range, it may easily be brought back. This is of especial importance when high grid pre-voltages are employed which may be the case in connection with conductometric titrations.

4. Finally, the compensation connection permits of the use of tubes of any type. Should a tube of low slope be desirable for special purposes (if. i., conductometry), it is only necessary to adapt the counter-current to the corresponding tube.

As anode battery a 100 to 120 volt storage battery of the Varta type is employed, and as electron-tube preferably the tube RE 354 of the Telefunkengesellschaft of Berlin, having a slope of 2.2. The sensitivity might be multiplied in future by improving the structure of the tube and employing more subtilized measuring devices.

An embodiment of my invention is illustrated in the annexed drawings of which Fig. 1 shows a diagrammatic view of thetitration vessel, the stirring device and the connections.

Fig. 2 is a circuit diagram of a complete assembly of titration vessel, electron tube measuring device and auxiliary sources of current, showing the plugging device for connecting the different electrodes and the measuring device.

Fig. 3, 4, 5 and 6 are fragmentary circuit diagrams illustrating the circuit connections established for different types of electrometric titrations.

The form of the titration vessel is so calculated as to afford the pomibility of treating small or large quantities in the same vessel.

From this calculation a pear-shaped bulb resulted as shown in Fig. 1. The calomel electrode was given a completely closed form substantially corresponding to a recently published suggestion of Hahn. The switch is soldered to the electrode and closed on both sides by plates of Jena-glass frit. It is immovably fixed by a guidingtubulure at the upper edge of the bulb and a notch in the bottom of the vessel. The electrode may be very small in an apparatus accordng to the invention, as no current is withdrawn therefrom.

The electrode is preferably inserted by means of a rubber plug into a tubulure at the bottom of the bulb in the form of a little circular plate. The indicator electrodes are mounted in tubes, in the form of little plates, having a diameter of about two fifths of an inch, at the bottom of the bulb by means of rubber plug's, the electrodes being disposed at the corners of a square so that the calomel and a silver electrode are placed at the ends of one diagonal line and two platinum electrodes at the ends of the other.

In any case, intense stirring is required to distribute each falling drop at once through the whole solution and to produce the uniform concentration upon whichthe potential depends.

The stirring motor is disposed. centrally above the opening of the bulb to render the implement as simple and transportable as possible. The stirrer itself is directly secured upon the motor shaft by'means of a very reliable conical chuck; it should turn without oscillation. 5

The stirrer should be finely regulable to stir large or small quantities with maximum velocity. This is easily attained by serially connecting the motor with an electric glow lamp of about 50 watts and in parallel with a resistance of 500 10 ohms. This construction protects the motor and the resistor against overloading and permits of the finest gradation of the stirring speed.

Referring now to the drawings, l is the pearshaped titration vessel provided with a feeding funnel 2 at the top and an outlet with stopcock 3 at the bottom. The electrodes are inserted through lateral tubulures l in the proximity of the bottom; one of the platinum electrodes is shown at 5 in Fig. 1. The tube 6 which communicates with the calomel electrode 1 is introduced through a tubulure at the top of vessel I, the ends being closed by plates 8 of Jena-glass frit. The exit of the burette 9 containing the titration solution and the stirrer III are introduced through another tubulure at the top of the bulb. The stirrer is driven by an electromotor I l which is fed by a 110 volt current connected in series with a 50 watt lamp l2 and controlled by a shunt resistor ll of 500 ohms. A circuit is conducted from the electrode 5 to the grid ll of the electron tube T, and another circuit from the calomel electrode I to one end of the heating filament IS. The main current'for heating the filament is derived from a storage battery I8 of about 4 volts and is regulated by an adjustable resistor H.

The anode current is produced by a storage battery l8 of 110 volts, the negative pole of which is connected with the one end of the heating fila- 40 ment, whereas the current goes from its positive pole through the milliammeter l9 to the anode 20 of the electron tube. The constant current in the milliammeter is compensated by a current in the opposite direction from the 2 volt battery 2| and this current is regulated by a resistor 22 of 500 ohms.

In Fig. 2, l indicates again the titration vessel provided with platinum electrodes 5a and 5b and the silver electrode 50. I is again the calomel electrode. From the four electrodes 50., 5b, 5c and 1 cables are conducted to the same number of plugs which may be distinguished by diflferent colors blue (5c), yellow (5a), yellow (51)), black (1). When not used these plugs are inserted into 55 idle sockets 23, 24, 25, 26. The connections are made by inserting the plugs into several of the sockets 21, 28, 29, 30, 3|, 32. The sockets 33, 34, 35 and 36 serve for connecting the anode battery, the heating current and the compensation currents.

The pairs of sockets 21, 3|, 32 and 29, are permanently connected by jumpers, socket 28 is wired to the negative side of the filament, and socket an is wired to the grid 14. An adjustable resistance 31 is connected between the socket 32 and the negative side of the filament and auxiliary sources of current, i. e. a direct current source 38 and an alternating current source 39, are provided with plug terminals for insertion in the appropriate sockets for diflerent types of analysis.

The plug terminal connections permit a rapid adjustment of the circuit network in accordance with the desired method of analysis. For greater clearness of illustration, the fragmentary diagrams, Figs. 3 to 6, omit the various elements which are not active, and the dotted lines indicate the several connections established between the several terminal plugs and sockets.

The circuit connections for oxidimetric analysis are indicated in Fig. 3, and comprise the connection of the calomel electrode cable plug to the grid socket 30 and the connection oi. a platinum electrode cable plug to the filament socket 28.

For argentometric analysis, as shown in Fig. 4, the calomel electrode is again connected to the grid socket 30 and the cable plug of the silver electrode 5c is inserted in the filament socket 28.

For conductometric analysis, the circuit connections of Fig. 5 are established by short-circuiting the sockets 29 and 30, thus connecting the grid to the filament through the adjustable resistance 31; the respective platinum electrodes 5a, 5b are connected to sockets 21, 28, and an alternating current voltage of from 15 to 20 volts is placed in series with these electrodes by connecting the current source 39 to the plugs 3|, 32.

For acidimetric analysis, Fig. 6, the current source 38 introduces a direct current potential of about 4 volts in series with the two platinum electrodes, the positive terminal of the current source being connected to socket 3| and the negative terminal over the resistance R. to socket 30. Electrodes 5a, 5b are connected to the sockets 21, 30

and the calomel electrode I is connected to the socket 28. y I claim:-

1. In a titration vessel for carrying out electrometric analyses by measuring the variations of the anode current of an electron tube operatively connected with said titration vessel, 9. calomel, a silver, and at least one platinum electrode insert ed in said titration vessel and adapted to be operatively connected with said electron tube.

2. In apparatus for carrying out electrometric analyses by measuring the variations of the anode current of an electron tube connected with a titration vessel, a substantially pear-shaped titration vessel provided with a stirrer, and a calomel, a silver, and at least one platinum electrode inserted near the bottom of said titration vessel and adapted to be operatively connected with said tube.

UDO EHRHARDT. 

